A/V receiver "calibration mics"... What are they really?

I'm sure we've all seen these things. My Harman Kardon receiver came with a nice looking transparent cone shaped calibration mic. Many receivers have mics for this purpose. This one plugs into the actual remote, and the signal is sent from the remote itself.

I'm curious as to what these microphones actually ARE. I wanna tear mine open and use the mic inside for a headphone measurement rig. To do that, I need to get a signal out of it, though. I assume it's just another electret condenser omni mic with calibration curve applied inside the receiver, right? If I can use this thing, I can just wire it up, plop the capsule into a plug, and stuff it into my ear!

I know people have used the the Audeyssey mics that come with some AVR for doing REW and basic correction, but it lacks a calibration file, unless soembody has made one out there. It works well enough with the receivers but I'm not sure the accuracy it would have in headphone measurment, the thread i've read on it beign used withe REW were mostly just for rough subwoofer integration.

My idea is to do a sweep through my monitors and measure it with my measurement mic, and then use the calibration mic in my ear in the same position as the measurement mic, do a sweep, and then make my own correction curve to make it as identical as possible.

Alright, that was very simple! I just took the mic capsule out and soldered it directly to the cable. Then I replaced the little jack with an XLR. Plugged it in, turned on phantom power, and I'm getting signal! Only needs to be hot glued and stuff, and it'll be ready to use!